patch secp256k1 to make sure it's libtoolized

Having "libtoolize --copy --force" first thing in "autogen.sh" is a
totally normal thing people do, it is supposedly harmless and
idempotent, no idea why lack thereof is apparently only problematic on
NixOS.

So: when running on NixOS, libtoolize.

WORKSPACE.bazel

@@ -279,6 +279,8 @@ versioned_http_archive(
     strip_prefix = "secp256k1-{version}",
     url = "https://github.com/bitcoin-core/secp256k1/archive/{version}.tar.gz",
     version = "694ce8fb2d1fd8a3d641d7c33705691d41a2a860",
+    patch_args = ["-p1"],
+    patches = ["//bazel/third_party/secp256k1:{version}.patch"],
 )
 
 versioned_http_archive(

bazel/third_party/secp256k1/694ce8fb2d1fd8a3d641d7c33705691d41a2a860.patch

@@ -0,0 +1,14 @@
+diff --git i/autogen.sh w/autogen.sh
+index 65286b9..edcbeb9 100755
+--- i/autogen.sh
++++ w/autogen.sh
+@@ -1,3 +1,9 @@
+ #!/bin/sh
+ set -e
++if [ -r /etc/os-release ]; then
++	. /etc/os-release
++	if [ "$NAME" = NixOS ]; then
++		libtoolize --copy --force
++	fi
++fi
+ autoreconf -if --warnings=all